18 



BOTANY 



PART I 



ellipsoidal shape (Fig. 8), and are scattered, in numbers, in the 

 parietal cytoplasm of the cells. All the chloroplasts in the Cormo- 

 phytes, and for the most part also in the green Thallophytes, have 

 this form. In the lower Algae, however, the chlorophyll bodies may 

 assume a band-like (Fig. 328 C\ stellate, or tabular shape. They are 

 often reticulately perforated, e.g. Cladophora (Fig. 9). In these cases 

 the chloroplast often includes one or more PYRENOIDS (Fig. 9 py) 

 these are spherical protoplasmic bodies containing an albuminous 

 crystalloid, and are surrounded by small grains of starch. No further 

 structure can be distinguished 

 in the living chlorophyll grains, 

 which have a uniformly green 

 colour. The green pigment, 



FIG. 8. Two cells from a 

 leaf of Funaria hygro- 

 metrica. cl, Chloroplasts; 

 n, nucleus. (x 300. 

 After SCHENCK.) 



FIG. 9. Reticulate chloroplast of Cladophora 

 arcta. py, Pyrenoids ; k, nuclei. (After 

 SCHMITZ.) 



chlorophyll, is essential for the decomposition of carbon dioxide in the 

 chloroplasts. 



The most recent investigations ( 15 ), especially those of WILLSTATTER and his 

 pupils, have shown that four pigments are present in the chloroplasts. There are 

 two closely related green pigments (chlorophyll a and &) in the proportions of 3 to 

 1, and two yellow pigments. The chlorophylls are esters of phytol, an alcohol of 

 the formula C 20 H 39 OH, and a tri-carbon acid. They are thus compounds with 

 large molecules containing carbon, oxygen, and hydrogen into the construction of 

 which nitrogen and magnesium enter, but not, as was previously assumed, either 

 phosphorus or iron. The blue-green CHLOROPHYLL a has the formula C 55 H 72 5 N 4 Mg, 

 while that of the yellow-green CHLOROPHYLL b is C 55 H 70 6 N 4 Mg. The yellow 

 pigments are the orange-red crystalline CAROTIN, hydrocarbons of the composition 

 C 40 H 56 , one of which also occurs in the root of the carrot arid the yellow crystalline 



